The entire סוגיא of מצוה לקיים דברי המת is a complicated one, and certainly cannot be covered, or even summarized, in one post. Here, I’m going to try and deal with a fairly limited aspect; specifically, the רמב”ם in הלכות מכירה in פרק ×›”ב, הלכה ט”ו / ט”×–.